This paper and long scientific investigation began, as many sound science questions do, somewhat by chance. In June 2014, time for the beginning of my PhD candidate career in Institute of Atmospheric Sciences, Chinese Academy of Sciences, I came to Zoige plateau to perform greenhouse gas (GHG) flux measurements in different alpine ecosystems, i.e., natural forest, grazed meadows and steppes as well as drained peatlands. It is the first time for me to get close in touch with peatland, a globally critically important ecosystem, later I knew through literatures, for preserving biodiversity, regulating hydrology, sequestering carbon (C) and mitigating climate change1,2. We observed that the drained alpine peatland was a weak source for methane (CH4)3 while a nonnegligible source for nitrous oxide (N2O)4,5. However, we totally ignored the potentially immense soil C release from this peatland due to water table decline, as large soil C stored in this ecosystem.
During my postdoc research in Institute of Meteorology and Climate Research-Atmospheric Environmental Research, Karlsruhe Institute of Technology, in Germany, I once again met across a large numbers of drainage ditches and drained peatlands during the field GHG measurements. Since then, I realized that drainage may be a widespread threat to global peatlands. Accordingly, I initiated a systematic literature survey on drainage activities and their impacts on the net ecosystem GHG balance of peatlands globally. We found that drainage resulted in the high emissions of N2O from European peatlands6, while caused significant reductions of net ecosystem production (NEP) by Tibetan alpine peatlands7. During the same period (2019–2022), scientists around the world also reported comparable results on drainage and GHG emissions from regional to global peatlands in Nature journals1,2,8–10.
Unfortunately, our literature survey showed that previous studies primarily focused on the significant changes in NEP, CH4 or N2O of pristine peatlands due to drainage1,2,8–10, however, the responses of soil respiration (SR), the second largest C flux between terrestrial ecosystems and the atmosphere after NEP11, in pristine peatlands to global drainage remain largely unknown. Furthermore, although it is well known that SR comprises heterotrophic respiration (HR) and autotrophic respiration (AR)12,13, another open question is whether the changes in SR due to global drainage were contributed by the changes in HR or AR or both, remains elusive. Disentangling the relative contributions of HR and AR to SR is crucial for understanding soil C dynamics because the former decomposes C that may have accumulated over millennia in the soil, whereas the latter represents the respiration of C recently assimilated by plants14,15. Consequently, the lack of clarity on this issue further limits the understanding of peatland soil C biogeochemistry, as HR is used to appropriately evaluate peat C decomposition and the PS rate (Rps) owing to peat C oxidation16.
Drainage has caused high Rps, which severely threatens the utilization of agriculturally drained peatlands if peat C is depleted due to oxidation16,17. However, the Rps is triggered by a combination of processes, such as physical compaction by heavy equipment or livestock trampling and shrinkage through the contraction of organic fibres when drying, consolidation by loss of water from pores in the peat, and oxidation due to the breakdown of peat C17,18. Therefore, disentangling the Rps from oxidation (i.e., HR) is crucial for the sustainable management of drained peatland, decelerating peat C loss, and mitigating soil CO2 release. However, the patterns of Rps by oxidation and associated total annual soil heterotrophic CO2 emissions from global drained peatlands are far from clear, underscoring the urgent need for assessments of the impacts of drainage to inform conservation guidelines for pristine peatlands and sustainable land-use policies for drained peatlands, as well as to reduce soil C losses for climate change mitigation.
According to our field investigations of extensive drainage activities in the Tibetan alpine peatlands in 2021 and literature review of widespread drainage activities across global peatlands, we believe that it is urgently to initiate a comprehensive assessment of drainage activities on SR and its components, HR and AR, and associated Rps from global peatlands. We do sincerely hope this work can contribute to reaching the consensus that conserving pristine peatlands and stopping drainage as well as restoring drained peatlands where possible to help mitigate climate change.
Driven by these motivations, we used meta-analysis and bootstrap upscaling approaches, world first time, studied drainage impacts on SR and its components, HR and AR, and associated Rps from global peatlands. We found that water table decline due to drainage and climate-induced drying resulted in significant increases in SR from pristine peatlands, mainly through HR rather than AR, and consequently intensified positive climate–carbon feedback and induced widespread global peat subsidence19. This relationship held across different climate zones and land uses19. We found that 81% (75–91%) of the total annual SR for all drained peatlands was attributable to tropical peatlands drained for agriculture and forestry and temperate peatlands drained for agriculture19. Globally, considerable amounts of peat organic matter were lost in the form of soil CO2 emissions from drained peatlands, contributing almost 14% (8.7–22%) of the total annual anthropogenic CO2 emissions from all land use changes or 4.6% (3.0–7.3%) of the total annual anthropogenic CO2 emissions from fossil fuel burning combined with land use changes19. Our findings highlight the critical importance of conserving pristine peatlands and restoring drained peatlands to help mitigate climate change.
Since 2022, funded by the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (Grant No. 2019QZKK0103) and "Double First-Class" Special Guidance Project of Lanzhou University (grant No. 561120206), our group has focused mainly on Tibetan alpine peatlands and performed comprehensive quantifications of drainage and restoration (through blocking drainage ditch) impacts on SR and its components, HR and AR, and net ecosystem exchanges of CO2, CH4 and N2O, as well as water storage and discharge in Tibetan alpine peatlands. We hope that our work can provide science-based guidelines for policy-makers and local communities to take actions to conserve pristine peatlands and restore drained peatlands to help preserve biodiversity, regulate hydrology, sequester C and mitigate climate change.
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- Deshmukh, C. S. et al. Conservation slows down emission increase from a tropical peatland in Indonesia. Nat. Geosci. 14, 484–490, (2021).
- Zhang, H. et al. Annual methane emissions from degraded alpine wetlands in the eastern Tibetan Plateau. Sci. Total Environ. 657, 1323–1333, (2019).
- Yao, Z. et al. Soil C/N ratio is the dominant control of annual N2O fluxes from organic soils of natural and semi-natural ecosystems. Agr. Forest Meteorol. 327, 109198, (2022).
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